The present invention relates to a controller for an internal combustion engine. A port injection valve, which injects fuel into an intake passage, and a direct injection valve, which injects fuel into a combustion chamber, each serve as a fuel injection valve supplying fuel into a cylinder. The internal combustion engine includes at least the port injection valve.
Japanese Laid-Open Patent Publication No. 2006-37744 discloses a controller for an internal combustion engine including a port injection valve, which injects fuel into an intake passage, and a direct injection valve, which injects fuel into a combustion chamber. The controller divides a request injection amount (EQMAX·klfwd), which is calculated based on an operating point of the internal combustion engine, between the port injection valve and the direct injection valve in accordance with an injection division ratio. When the injection division ratio is changed to increase the ratio of the injection amount of the port injection valve, the controller performs an increase correction on the port injection amount. This process is performed based on a consideration that an increase in the ratio of the injection amount of the port injection valve causes a larger amount of fuel to collect on the intake passage and therefore decreases the amount of fuel flowing into the combustion chamber from the port injection valve. In other words, the process is performed based on a consideration made to a situation in which the air-fuel ratio of an air-fuel mixture, which is subject to combustion in the combustion chamber, is leaner than the target value.
In addition to avoiding a situation in which the air-fuel ratio is excessively lean in the combustion chamber by performing the increase correction on the port injection valve, to avoid a situation in which the actual air-fuel ratio is richer than the target value, a necessary increase correction amount needs to be obtained with high accuracy. However, an increase correction amount obtained by the controller generally has an error. Thus, when the increase correction is performed on the port injection valve, the controllability of the air-fuel ratio in the combustion chamber may be lowered.
The above problem is not limited to an internal combustion engine that includes a port injection valve and a direct injection valve. The problem also occurs, for example, in an internal combustion engine that injects fuel from an injection port valve before the intake valve opens and then again injects fuel when the intake valve is open and also divides the request injection amount between two injections and changes the ratio of the injection amount. In this case, when the ratio of the amount of fuel injected from the port injection valve before the intake valve opens is increased, a larger amount of fuel collects on the intake passage. Thus, the air-fuel ratio of the air-fuel mixture in the combustion chamber may become leaner than the target value. Additionally, when the increase correction is performed to avoid the air-fuel ratio from becoming lean, an error in the increase correction may lower the controllability of the air-fuel ratio.